Patients with sickle cell nephropathy are living longer. Unfortunately, many of them suffer from major organ system failure including heart, lung, and kidney disease. As many as one-fifth of the sickle cell population have abnormal amounts of protein in their urine and between 5 to 18% of patients have renal insufficiency. The cause of this renal dysfunction is attributed to a glomerular abnormality. This glomerular lesion is due to focal and segmental glomerulosclerosis in the setting of glomerular hypertrophy. Angiotensin II converting enzyme inhibitor therapy appears to diminish proteinuria, and perhaps ameliorate renal insufficiency in other glomerular diseases in particular diabetic nephropathy. Preliminary studies have demonstrated that short term therapy with an angiotensin II converting enzyme inhibitors decreases protein excretion in patients with biopsy-proven sickle cell nephropathy. We propose to test the hypothesis that the long-term administration of an angiotensin II converting enzyme inhibitor to patients with sickle cell disease and proteinuria (1) prevents or retards the development of renal insufficiency, and (2) reduces proteinuria on a long-term basis. We propose to test this hypothesis in a prospective, randomized, controlled study analyzing the effects of an angiotensin II converting enzyme inhibitor when compared to placebo in patients with sickle cell disease and established proteinuria.